Hot bolting is the sequential replacement of flange bolts (stud bolts and nuts) on a pressurized, in-service piping system to restore joint integrity without shutting down the line. It is a controlled maintenance technique used to address flange leaks caused by bolt relaxation, corrosion, or gasket degradation, and it is governed by site-specific procedures aligned with ASME PCC-2 (Repair of Pressure Equipment and Piping).
When Hot Bolting Is Used
Scenario
Description
Bolt corrosion
External corrosion has reduced bolt cross-section below minimum requirements
Bolt relaxation
Bolts have lost preload due to creep, vibration, or thermal cycling; joint is leaking
Gasket seating
Re-torquing existing bolts cannot restore gasket sealing; fresh bolts and controlled torque are needed
Planned maintenance
Proactive replacement of degraded bolts during a maintenance window without full shutdown
Hot Bolting Procedure
Step
Activity
Notes
1
Obtain work permit and hot bolting procedure approval
Requires engineering assessment, risk assessment, and operations authorization
Prepare replacement bolts (same specification and grade as original)
New stud bolts and nuts per ASME B16.5 or project specification; lubricate threads
4
Install leak containment and PPE
Clamp or seal around flange; full-face shield, chemical-resistant gloves, fire watch if flammable service
5
Remove one bolt at a time using hydraulic torque wrench
Never remove more than one bolt simultaneously; start with the bolt showing the least corrosion
6
Inspect bolt hole, flange face, and gasket condition
Look for erosion, pitting, or gasket blowout; document findings
7
Install new bolt and hand-tighten nut
Ensure bolt length, grade marking, and thread engagement are correct
8
Torque the new bolt to the specified value
Use calibrated hydraulic torque wrench; record torque value
9
Move to the next bolt in the sequence
Follow a diametrically opposite (star) pattern around the flange
10
After all bolts are replaced, perform a final pass torque on all bolts
Apply target torque in star pattern; verify zero leakage
11
Monitor joint for 24-48 hours
Check for leaks after thermal cycling; re-torque if necessary
Key Safety Requirements
One bolt at a time: The remaining bolts must maintain sufficient clamping force to contain the system pressure. Engineering calculations per ASME PCC-2 must confirm that the joint can sustain the operating load with one bolt removed.
Hydraulic tooling: Use hydraulic torque wrenches (not impact wrenches) for controlled and accurate bolt tensioning. Impact tools create shock loads that can disturb adjacent bolts.
Exclusion zone: Establish a safety perimeter around the flange joint. Only authorized personnel may be within the zone during bolt removal.
Fire watch: Mandatory for flammable or combustible services. Keep fire extinguishing equipment within immediate reach.
Bolt material traceability: New bolts must have material test certificates (EN 10204 3.1 or equivalent) and must match the original specification.
Hot Bolting vs. Hot Torquing
Activity
Description
When Used
Hot bolting
Sequential removal and replacement of bolts on a live joint
Bolt corrosion, degraded bolts, bolt breakage
Hot torquing
Re-torquing existing bolts to restore preload without replacing them
Bolt relaxation without material degradation
Hot bolting activities are documented as part of the piping inspection and maintenance records, with torque values, bolt traceability, and leak test results retained for the life of the asset.
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